Overview
This lecture explains acids, bases, and the concept of pH, detailing how pH indicates acidity or basicity and how to measure it with indicators.
Acids and Bases: Definitions and Properties
- Acids are substances that taste sour, feel sticky, and produce H+ (hydrogen ions) in aqueous solutions.
- Acids conduct electricity due to freely moving charged particles (ions).
- Acids can corrode stones and metals.
- Bases taste bitter, feel slippery, and produce OH- (hydroxide ions) in aqueous solutions.
- Bases also conduct electricity and can break down oil and grease, making them useful in soaps.
Understanding pH and the pH Scale
- pH measures how acidic or basic a solution is by indicating the concentration of H+ in solution.
- The pH scale ranges from 0 (very acidic) to 14 (very basic), with 7 as neutral.
- Acids have pH less than 7; bases have pH greater than 7.
- The pH scale is logarithmic: each step is a 10-fold difference in H+ concentration.
- More acidic solutions have a lower pH due to higher H+ concentration.
Methods to Measure pH
- pH meters directly measure H+ concentration using voltage; they are accurate but expensive.
- pH indicators change color based on solution acidity or basicity.
- Litmus paper is a simple indicator: red for acidic, blue for basic solutions.
- Blue litmus turns red in acids; red litmus turns blue in bases.
- Litmus tests only indicate acidic or basic, not the degree.
- pH paper and universal indicators show a range of colors, revealing how acidic or basic a solution is.
Key Terms & Definitions
- Acid — substance that produces H+ ions in water and has pH < 7
- Base — substance that produces OH- ions in water and has pH > 7
- pH — measure of hydrogen ion (H+) concentration, indicates acidity/basicity
- pH scale — scale from 0 to 14 for acidity/basicity; 7 is neutral
- Litmus paper — indicator that turns red in acids, blue in bases
- Universal indicator — a mixture of indicators that shows a range of colors for different pH values
Action Items / Next Steps
- Practice identifying acids and bases using pH paper or litmus tests.
- Review examples of acids and bases and their typical pH values.
- Complete any assigned reading on acid-base indicators and pH measurement techniques.